The Interspecific Competition Between Larvae of Aedes aegypti and Major African Malaria Vectors in a Semi-Field System in Tanzania

Abstract

Interspecific competition between mosquito larvae may affects adult vectorial capacity, potentially reducing disease transmission. It also influences population dynamics, and cannibalistic and predatory behaviors. However, knowledge of interspecific competition between Ae. aegypti and Anopheles species is limited. The study examined interspecific competition between Ae. aegypti larvae and either An.arabiensis, An. gambiae, or An. funestus on individual fitness in semi-field settings. The experiments involved density combinations of 100:100, 200:0, and 0:200 (Ae. aegypti: Anopheles), reared with and without food, in small habitats (8.5 cm height × 15 cm diameter) with 0.5 liters of water and large habitats (15 cm height × 35 cm diameter) with 1 liter of water. The first group received Tetramin^® fish food (0.02 g), while the second group was unfed to assess cannibalism and predation. While interspecific competition affected both genera, Anopheles species experienced greater effects, with reduced survival and delayed development, compared to Ae. aegypti. The mean wing lengths of all species were significantly small in small habitats with a mixed population (p < 0.001). The presence of food reduced cannibalism and predation compared to its absence. These interactions have implications for diseases transmission dynamics and can serve as biological indicators to signal the impacts of vector control interventions.

Keywords: Aedes aegypti; An. arabiensis; An. funestus; An. gambiae; cannibalism; interspecific competition; intraspecific competition; predation.

Figure 1

Schematic presentation of the experimental setup and procedures for inter and intraspecific competition between Aedes aegypti and either Anopheles arabiensis, Anopheles gambiae, and Anopheles funestus in small and large habitat sizes.

Figure 2

(A) Artificial larval habitats consisting of small and large plastic basins used for larval rearing. (B) Daily monitoring of larval survival, including counting of alive larvae, dead larvae, missing larvae, alive pupae, and dead pupae. (C) Collected pupae were transferred to small plastic bowls with water and placed in net cages for adult emergence. (D) Emerged mosquitoes were taken to the laboratory for wing size measurement. (E) Wing size observed under a microscope as a proxy for adult body size.

Figure 3

Mean percent (95% CI) of larvae survived to adulthood for (A) Aedes aegypti and Anopheles arabiensis, (B) Aedes aegypti and Anopheles gambiae, and (C) Aedes aegypti and Anopheles funestus exposed in single and mixed population across small and large habitats. Bar graphs without error bars indicate extremely narrow confidence intervals.

Figure 4

Mean (95% CI) wing length of female (A) Aedes aegypti with Anopheles arabiensis, (B) Aedes aegypti with Anopheles gambiae, and (C) Aedes aegypti with Anopheles funestus in single and mixed population across different habitat size.

Figure 5

Mean percent (95% CI) of missing larvae in both absence and presence of food for (A,B) Aedes aegypti and Anopheles arabiensis, (C,D) Aedes aegypti and Anopheles gambiae, and (E,F) Aedes aegypti and Anopheles funestus exposed in single and mixed population across small and large habitats. Bar graphs without error bars indicate extremely narrow confidence intervals.